1. Field of the Invention
The present invention relates to a power diver/combiner for dividing or combining mainly high-frequency signals in a microwave band and a millimeter-wave band.
2. Description of the Related Art
A conventional power divider/combiner will be described with reference to the drawings. FIG. 11 is a diagram showing a circuit configuration of the conventional power divider/combiner reported in, e.g., xe2x80x9cFoundations for Microwave Engineering Second Edition,xe2x80x9d written by R. E. Collin, McGraw-Hill International Editions Electrical Engineering Series, p445, McGraw-Hill Inc., 1992.
Referring to FIG. 11, there are shown an input line 10, output terminals 2, a branch line 3 with an electrical length being a xc2xc wavelength, of which one end is connected at a diverging point 31 to the input line 10 and the other ends are connected to the output terminals 2, an isolation resistor 5 connected to between the output terminals 2, and load impedances 21 connected to the output terminals 2.
Next, an operation of the conventional power divider/combiner explained above will be described with reference to the drawings. FIG. 12 is a diagram showing how the prior art power divider/combiner operates.
The high-frequency signal inputted to the input line 10 is divided at the diverging point 31 to the branch lines 3. The signals assuming the same phase and having an equal amplitude flow to the output terminals 2 which are therefore take an equal electric potential, while no current flows to the isolation resistor 5.
At that time, the branch lines 3 function as a xc2xc wavelength impedance transformer, whereby an impedance as viewed from the input line 10 toward the output terminals 2 side is equal to a characteristic impedance of the input line 10, and the high-frequency signal is divided without causing any reflection.
On the other hand, the high-frequency signals, when inputted to the output terminals 2, are combined at the diverging point 31 and thus outputted to the input line 10.
Further, even when there is a difference in potential between the output terminals 2, as shown in FIG. 12, a high-frequency signal A (xc2xc+xc2xc=xc2xd wavelength delay) flowing through one of the branch lines 3 from one of output terminals 2 and a high-frequency signal B (with no delay) flowing to the isolation resistor 5, become opposite in phase and equal in amplitude at the other output terminal 2, and are therefore offset each other. As a result, the current flows to the isolation resistor 5 and is absorbed, and the isolation between the output terminals 2 is ensured.
In the conventional Wilkinson type power divider/combiner described above, a passing phase of the isolation resistor 5 is required to be zero in order to ensure the isolation between the output terminals 2. If a thin film resistor is used as the isolation resistor 5, however, a length of the resistor can not be ignored as compared with the wavelength of the high-frequency signal, and the high-frequency signals A, B shown in FIG. 12 do not assume the opposite phases. Therefore, the signal inputted to one of output terminals 2 is not offset at the other output terminal 2, and there arises a problem in that the isolation between the output terminals 2 declines.
Further, when viewed from the input terminal 10, the isolation resistor 5 having the electrical length appears as a open stub, and hence there also exists such a problem that an I/O reflection characteristic declines.
It is a primary object of the present invention, which was devised to obviate the problem described above, to provide a power divider/combiner capable of ensuring an isolation between output terminals even with using of an isolation resistor having a length that can not be ignored as compared with a wavelength of a high-frequency signal in use, and exhibiting an excellent I/O reflection characteristics.
To accomplish the above object, according to a first aspect of the present invention, there is provided a power divider/combiner comprising an input terminal; two output terminals, two branch lines each connecting the input terminal and the output terminal and having a line length that is xc2xc of a set wavelength or a multiple of integer of half a wavelength and xc2xc of the set wavelength, an isolation resistor connected to between the output terminals, and a transmission line interposed between each of the output terminals and the branch lines.
The power divider/combiner according to a second aspect of the present invention may further comprise a capacitance element having one end connected to the input terminal and the other end grounded.
The power divider/combiner according to a third aspect of the present invention may further comprise a open stub connected to the input terminal.
The power divider/combiner according to a fourth aspect of the present invention may further comprise a low impedance line interposed between the input terminal and a connecting point between the two branch lines.
In the power divider/combiner according to a fifth aspect of the present invention, the isolation resistor may be connected between the output terminals through a connection line.
According to a sixth aspect of the present invention, there is provided a 2-way power divider/combiner constructed by connecting at multi-stages the 2-way power dividers/combiners according to the second through fifth aspects of the invention, wherein the 2-way power dividers/combiners disposed at the second stage onward are provided with neither the capacitance element, nor the open stub, nor the low impedance line.